Assigkmob



H. W. NICHOLS.

RADIO TRANSMISSION.

' APPLICATION HLED SEPT.1, 1915. RENEWED JAN. 2.1920.

1,422,882. 4 Patented July 18,1922;

UNITED STATES PATENT OFFICE.

HAROLD NICHOLS, O3] ldAPLEVIOOD, NEXVJ ERSEY, ASSiGNOR, B)? MESNE ASSIGN- MENTS, T0 COMPANY, INCORPORATED, CQRPORATION 0 new Your.

RADIO TEANSMISSION.

I Specification of Letters Patent. Patented J l 18 15322 Application filed September 1,1915, Serial No. 48,452. Renewed January 53, 1920. Serial No. 348,880}.

To aZZ whom it may concern Be it known that I, Harte-Ln WILLIAM NICHOLS, a citizen oi the United States, residing at lvlaplewood, inthe county of Essex and State of New Jersey, have invented ertain new and useful Improvements in Radio Transmission, of which the following is a tall, clear, concise, andeiract descrlption. w

This invention relates to the art of transmitting signals by means of high-trequency electrical waves.

Its object is to vary or modulate the amplitude oi radiated. high-frequency waves in accordance with the wave form of signals to be transmitted. Its object is also to accomplish this modulation without requiring that the telephone transmitter, telegraph key or other primary source of modulated power shall handle all the power required to be modulated.

A further object of this invention is to modulate the radiated power in an ellicient manner by correct proportioning of the impedances of the system.

These objects are accomplished by making use of the fact that in athermionic amplifier of the audion type, the impedance of the output circuit depends upon and varies with the voltage impressed upon the input circuit, and that the changes in power output, due to such changes in impedance, are much larger than the power input required to produce them. On account of this property, it is obvious that i'lf the an tenna current made to How through the output circuit of an amplifier, large variations in the power radiated from the an* tenna may be produced without using excessive power in the primary modulating source, and therefore permitting the use of a commercial telephone transmitter or telegraph key as this primary source.

It has been found, however, that the impendance of the output circuit of the vacuum tube ampli er as at present constructed, is so high that it cannot be inserted directly into the antenna without seriously decreasing the current in the antenna and consequently the radiating power of the tran mitting system. In order that modulation shall be most efficiently carried out, it is necessary that the impedance of the modulating device shall. be comparable with the,

other impedances in circuit with it, and to accomplish this correct proportioning ot' impedances, this invention proposes to insert the vacuum tube as a shunt upon some impedance in the antenna which is compan able with that of the tube. In this way only a -traction, for example one hall, of the antenna power is carried by the vacuum tube. For example, in a simple tuned system consisting of an inductance coil and a condenser in series, the impedance between the extreme terminals of this circuit is small, since the system is tuned. On the other hand, the impedance between the two terminals of the coil or that between the two terminals of the condenser, may be made large by sharply tuning the resonant system. In order therefore, to modulate the current in such a system by means of a high impedance modulating device, it would be necessary to connect the high impedance device across the terminals of the coil or the condenser, but not across the extreme terminals of the circuit. in the present invention, therefore, the antenna is tuned ,las sharply as may be desired for eliicient transmission of signals, and the thermionic amplifier is shunted across only a portion of the antenna, said portion having preferably an impedance of the same order of magnitude as that of the amplifier.

The exact nature of this invention will be better understood by reference to the drawings, in which Fig. 1 represents one method o'l" matching the impedances concerned; Fig. 9, shows a method of connection in which the effective impedance of an inductance coil is varied; Fig. 3 shows a similar method :lor varying the eifective impedance of a condenser in the antenna. circuit; and Fig. shows another method Oil placing the amplifier effectively in shunt to part of the antenna by using a transformer. In all of these figures the same numerals denote corresponding parts.

Referring to Fig. l, 1-2 is an antenna containing coil 3 and condenser at in parallel. 5 is another coil inserted into the an tenna and coupled to coil 6, which is supplied with power by means of the highiirequency generator 16, which therefore serves to energize the antenna. The object of using the parallel arrangement 8, 4: of coil and condenser is to secure an impedance of the same order of magnitude as that of the output circuit of the amplifying system shunting it. 7 is a thermionic repeater of the audion type containing plate 8, grid 9 and filament 10. 11 is a battery or other source of direct current inserted in the out put circuit as usual in the operation of such amplifiers. Battery 12 serves to heat the filament 10. It will sometimes be necessary, in order to handle all the power required in the modulating system, to use a plurality of thermionic elements connected in parallel as shown in this figure. 13 is a transformer by means of which variations in voltage caused by microphone 14 are impressed upon the input circuit of the amplifying system. 15 is a battery supplying current to microphone 141.

In the system as shown in this drawing, the effective impedance of the parallel arrangement 3, 4: is varied by the amplifier as discussed in the first part of this specification.

Fig. 2 differs from Fig. 1 only in that the thermionic amplifier is shunted across the coil 5, which is also usedin connection with coil 6 and generator 16 to impress power upon the antenna. In the circuit arrangement of this drawing, if the antenna is sharply tuned the impedance of the coil will be comparable with that of the ampliier.

In the arrangement of Fig. 8, modulation is accomplished by placing a variable shunt upon the condenser 4 inserted directly in the antenna circuit. In this figure, in order that the output circuit of the amplifier may be supplied with current, it is necessary to shunt the condenser with the choke coil 17. The impedance of this choke coil to liigh-frequency' currents is so large that practically none of the antenna current passes through it, while at the same time it offers unobstructed passage to direct current in the output circuit of the amplifier. This choke coil also serves another purpose in that it allows the discharge of accumulated electricity on the antenna, such accumulated charges being otherwise prevented from flowing to ground by the condenser 4c.

In Fig. 4 this thermionic shunt is placed directly on the generator 16, but since generator and amplifier are coupled to the antenna by transformer 5-6, the effect, for

forced oscillations, is the same as if the parallel arrangement of generator and amplifier (in general with modified impedance) were inserted directly in the antenna. Owing to the fact that this circuit is not so flexible as the others shown, it will not in general be as desirable as one of the others.

Although this invention is described par ticularly as applying to a wireless transmitting system, it will be understood that the antenna may be replaced by a portion of a wire circuit, for example, a telephone line, without departing from the broad idea underlying this invention. I, therefore, desire not to be limited to a wireless transmitting system, but intend this invention to apply to the use of the modulating apparatus here described in connection with a wire system, as well as with a wireless system.

What is claimed is:

1. In a radio transmission system, an antenna, a source of high-frequency power supplying said antenna, a thermionic discharge path arranged to carry a fraction of the power for said antenna, a source of waves of signaling frequencies, and means for varying the power carried over said thermionic path in accordance with said waves.

2. In a signaling system, an antenna including an impedance element, an electrical discharge device in shunt to said element, said impedance element and said electrical discharge device having impedances of the same order of magnitude, and means in said antenna in series with said element for setting up a high frequency electromotive force in said antenna.

3. A signaling system comprising a transmission circuit, means in said circuit for supplying high frequency current thereto, an impedance element in said circuit in series with said means, and a thermionic element in shunt to said impedance element, said thermionic element and said impedance element having impedances of the same order of magnitude. v

In witness whereof, I hereunto subscribe my name this 28th day of August A. D.,

HAROLD W. NICHOLS. 

